Compressor unit

ABSTRACT

A compressor unit includes a motor and a compressor in a casing of a gastight form. The casing houses the motor and the compressor. The motor includes a rotor surrounded by a stator which has an encapsulation formed on the inner diameter as a separating can, so that a medium being handled does not damage the stator. The separating can includes a polymer matrix which is reinforced using a plurality of fibers. The polymer matrix is at least partly a ceramic fiber reinforced polymer matrix. The plurality of fibers are formed as continuous filaments. The continuous filaments include the length of at least 30 mm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of the US patent application filed onMar. 18, 2010, and assigned application Ser. No. 12/678,843, which isthe US National Stage of International Application No.PCT/EP2008/062526, filed Sep. 19, 2008 and claims the benefit thereof.The International Application claims the benefits of European PatentOffice application No. 07018541.8 EP filed Sep. 21, 2007. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a compressor unit, particularly to a compressorunit having a motor with a separating can.

BACKGROUND OF INVENTION

Turbomachines and their electrical drive motors are usually housed inseparate casings. As a result, shaft seals intended to prevent the fluidthat is handled from leaking to the outside are required in theturbomachines.

The turbomachine and the drive motor can be housed in a casing without ashaft seal if a separation between the rotor, which comes into contactwith the fluid, and the stator takes place in the electric motor bymeans of a tubular component. Because of its position in the air gap,the component is referred to as a “separating can”.

Previously used separating cans have one or more of the followingdisadvantages:

a) Electrical conductivity: the separating can heats up due to eddycurrents. The heat must be removed and the overall performance of themachine is very limited.

b) Low strength: the separating is only able to withstand smalldifferences between internal pressure and external pressure. Thetechnique is not suitable for high-pressure machines.

c) The production technology only allows a small overall height of theseparating can, as a result of which the overall size of the machine isrestricted.

It has previously only been possible for small machines (particularlypumps) of relatively low output to be constructed with a separating canor split case. The following materials have previously been used forthis:

a) Metallic special or superalloys, such as Hastelloy or Inconel

(Disadvantage: the electrical conductivity induces eddy currents, whichwould unacceptably reduce the efficiency of high-performancecompressors)

b) CRP, carbon fiber reinforced plastics

(Disadvantage: the carbon fiber also still has an excessively highelectrical conductivity, which would greatly reduce the efficiency ofhigh-performance compressors—on account of the induced eddy currents)

c) Particle or glass fiber reinforced and unreinforced high-performancepolymers (e.g. FORTRON from the Ticona company)

(Disadvantage: the achievable stiffness and strength are much too lowfor use in high-pressure compressors)

d) Monolithic technical ceramic such as zirconium dioxide (e.g. FRIALITfrom the Friatec company)

(Disadvantage: previously when producing split cases, ceramic powder wasfirst pressed cold-isostatically (green compact) and subsequentlysintered. The sintering process thereby causes a shrinkage of 18-25% andstrength-reducing structural defects. Moreover, when sintering verylarge split cases—as are required for high-pressurecompressors—mass-related deformations would occur, even the formation ofcracks. For these reasons, it has not previously been possible toproduce separating cans or split cases with a length significantly above300 mm from one piece. Moreover, the damage tolerance achievable bymeans of this production method under pressures of up to 150 bar is toolow).

DE 20 2004 013 081 U1 discloses a separating can which consists of aceramic or glass-like material. DE 200 07 099 U1 and US 2003/193260 A1describe sintered ceramic separating cans. Such separating cans are toobrittle for the intended use. A separating can described in U.S. Pat.No. 6,293,772 B1 consists of a fiber reinforced polymer matrix, whichmay in particular have polymer fibers and be reinforced by means ofceramic.

In the same way, DE 38 23 113 C1 and U.S. Pat. No. 4,952,429 A discloseprotection from abrasion, particularly superficial protection, by meansof ceramic particles, for example zirconium oxide. Split cases withpartly ceramic contents are also described in DE 39 41 444 A1, DE 197 44289 A1 and DE 34 13 930 A1. All of the solutions presented do notsufficiently satisfy the set of requirements described above, inparticular with regard to the elasticity and strength requirements.

SUMMARY OF INVENTION

It is therefore an object of the invention to provide a compressor unitwith a motor having a separating can which is able to withstand highpressure differences and a method for producing the same.

The above object is achieved by the features of the independentclaim(s). The back-referenced claims comprise advantageous developments.

The separating can may also be produced by correspondingly suitableceramic fibers being wound in suitable orientation onto a mandrel whilea binder is added, it being possible for the binder to consist of aceramic or glass-like powder or a slip of a ceramic/glass-like powder,and the binder sinters or fuses together as a result of subsequent heattreatment, which may take place in the atmosphere or in air or in an HIPinstallation.

In this case, the process may either be conducted in such a way that thewound fiber body is initially only provided with a basic mechanicalstrength, and may still undergo mechanical processing, or that theseparating can is provided right away with the required strength andsealing integrity for the application.

As an alternative to this, the sealing integrity may be achieved by thepores of the heat-treated fiber body being closed after the processdescribed above. This may take place, for example, by high-pressureinfiltration with liquid glass or by an enameling process involvingimmersion in a liquid slip (frit) and subsequent firing or glazing ofthe surface or by other suitable processes.

Disadvantages of previous separating can constructions can be avoided ifa separating can of a ceramic fiber reinforced polymer matrix is used.Silicon carbide fibers or high-purity aluminum oxide fibers or zirconiumdioxide fibers or else mullitic fibers may be used, inter alia, forthis. All these fibers provide high tensile load-bearing capacity. Theload-bearing capacity can be further increased if the type ofinterlinkage of the fibers is optimized, in particular if short fibersthat preferably have a length of between 0.1 mm and 1 mm, or randomfibers or continuous filaments that are preferably at least 30 mm long,or bundles of fibers (rovings) and fiber mats (woven or laid structures,etc.) are used. The abrasion resistance of the polymer matrix can beadvantageously increased if the surface of the separating can is alsoadditionally interspersed or coated with ceramic particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below on the basis of aspecific exemplary embodiment with reference to drawings, in which:

FIG. 1 is a schematic representation of a longitudinal section through acompressor unit with a separating can according to the invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 schematically shows a section along a compressor unit 1, whichhas as essential components a motor 2 and a compressor 3 in a casing 4of a gastight form. The casing 4 houses the motor 2 and the compressor3. In the region of the transition from the motor 2 to the compressor 3,the casing 4 is provided with an inlet 6 and an outlet 7, with fluidthat is to be compressed being sucked in through the inlet 6 by means ofan intake stub 8 and the compressed fluid flowing out through the outlet7.

The compressor unit 1 is arranged vertically during operation, a motorrotor 15 of the motor 2 being combined with a compressor rotor 9 of thecompressor 3 to form a common shaft 19, which rotates about a commonvertical axis of rotation 60.

The motor rotor 15 is mounted in a first radial bearing 21 at the upperend of the motor rotor 15.

The compressor rotor 9 is mounted by means of a second radial bearing 22in a lower position.

At the upper end of the common shaft 19—that is to say at the upper endof the motor rotor 15—an axial bearing 25 is provided.

The compressor 3, formed as a centrifugal compressor, has threecompressor stages 11, which are respectively in connection with anoverflow 33.

The electromagnetic bearings 21, 22, 25 are cooled to operatingtemperature by means of a cooling system 31, the cooling system 31providing a tap 32 in an overflow of the compressor 3. From the tap 32,part of the medium being handled, which is preferably natural gas, isdirected through a filter 35 and subsequently passed through twoseparate pipelines to the respectively outer bearing locations (firstradial bearing 21 and fourth radial bearing 24 as well as axial bearing25). This cooling by means of the cold medium being handled 80 dispenseswith the need for additional supply lines.

The motor rotor 15 is surrounded by a stator 16, which has anencapsulation formed on the inner diameter as a separating can 39, sothat the aggressive medium being handled 80 does not damage windings ofthe stator 16. The separating can 39 is designed here in such a way thatit is able to withstand the full operating pressure. This is alsobecause the stator is provided with separate cooling 40, in which adedicated cooling medium 56 circulates. A pump 42 provides a circulationhere via a heat exchanger 43. At least the separating can 39 isconfigured in such a way that the portion that extends between thestator 16 and motor rotor 15 has a thin wall thickness but isnevertheless capable of withstanding the design pressure when the statorcooling 40 is completely filled with the cooling medium 56. In this way,relatively great eddy current losses in this region are avoided and theefficiency of the overall arrangement is improved.

1. A compressor unit, comprising: a motor and a compressor in a casingof a gastight form, wherein the casing houses the motor and thecompressor, wherein the motor comprises: a stator, a rotor surrounded bythe stator, and a separating can which forms an encapsulation on aninner diameter of the stator so that a medium being handled by thecompressor unit does not damage the stator, the separating cancomprising: a polymer matrix which is reinforced using a plurality offibers, wherein the polymer matrix is at least partly a ceramic fiberreinforced polymer matrix, wherein the plurality of fibers are formed ascontinuous filaments, and wherein the continuous filaments include thelength of at least 30 mm.
 2. The compressor unit as claimed in claim 1,wherein the plurality of fibers comprise silicon carbide.
 3. Thecompressor unit as claimed in claim 1, wherein the plurality of fiberscomprise aluminum oxide.
 4. The compressor unit as claimed in claim 1,wherein the plurality of fibers comprise zirconium dioxide.
 5. Thecompressor unit as claimed in claim 1, wherein a surface of theseparating can is interspersed with a plurality of ceramic particles. 6.The compressor unit as claimed in claim 3, wherein the surface of theseparating can is interspersed with a plurality of ceramic particles.